From: Tom Lane Date: Mon, 18 Mar 2013 17:34:27 +0000 (-0400) Subject: Improve documentation of EXTRACT(WEEK). X-Git-Tag: REL9_1_9~17 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=4400976281d07b880c5c311c55e9ec95805b3c66;p=postgresql Improve documentation of EXTRACT(WEEK). The docs showed that early-January dates can be considered part of the previous year for week-counting purposes, but failed to say explicitly that late-December dates can also be considered part of the next year. Fix that, and add a cross-reference to the "isoyear" field. Per bug #7967 from Pawel Kobylak. --- diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 264fe110c0..5f32d74fff 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -6919,16 +6919,19 @@ SELECT EXTRACT(SECOND FROM TIME '17:12:28.5'); The number of the week of the year that the day is in. By definition - (ISO 8601), the first week of a year - contains January 4 of that year. (The ISO-8601 - week starts on Monday.) In other words, the first Thursday of - a year is in week 1 of that year. + (ISO 8601), weeks start on Mondays and the first + week of a year contains January 4 of that year. In other words, the + first Thursday of a year is in week 1 of that year. - Because of this, it is possible for early January dates to be part of the - 52nd or 53rd week of the previous year. For example, 2005-01-01 - is part of the 53rd week of year 2004, and 2006-01-01 is part of - the 52nd week of year 2005. + In the ISO definition, it is possible for early-January dates to be + part of the 52nd or 53rd week of the previous year, and for + late-December dates to be part of the first week of the next year. + For example, 2005-01-01 is part of the 53rd week of year + 2004, and 2006-01-01 is part of the 52nd week of year + 2005, while 2012-12-31 is part of the first week of 2013. + It's recommended to use the isoyear field together with + week to get consistent results.